A bumper beam is provided inside of a bumper of a vehicle. This is to allow the bumper beam to bear an impact load upon collision, thereby ensuring safety of the vehicle. In particular, large energy is generated upon frontal collision in an automobile or the like. On the other hand, in recent years, from the viewpoint of reducing CO2 and improving fuel economy, there is a demand for weight reduction of a bumper beam. To realize weight reduction of a bumper beam, it is necessary to improve strength of the bumper beam while reducing the plate thickness of the bumper beam.
To enhance the strength of a bumper beam, a bumper beam reinforced by a reinforcing member has been proposed (for example, Japanese Patent Application Publication No. 7-309184 (Patent Literature 1), Japanese Patent Application Publication No. 6-328988 (Patent Literature 2), and Japanese Patent Application Publication No. 6-171441 (Patent Literature 3)).
In a bumper beam disclosed by Patent Literature 1, a reinforcing member is disposed in a box-shaped space formed by multiple joined members. The reinforcing member lies in a fore-and-aft direction of vehicle. Patent Literature 1 states that it is thereby possible to achieve an equivalent strength of the bumper beam compared with that of a conventional bumper beam, as well as to realize weight reduction and cost reduction.
A bumper beam disclosed in Patent Literature 2 has a box-shaped cross section, and a reinforcing member inside of the box-shaped cross section. The reinforcing member lies in the up-and-down direction of a vehicle. Therefore, when a load is applied in the fore-and-aft direction of the vehicle, outward deformation of an upper wall section and a lower wall section is suppressed. Patent Literature 2 states that this enhances the strength of the bumper beam.
A bumper beam disclosed in Patent Literature 3 has a box-shaped cross section formed by combining hat-shaped press formed parts, and has a reinforcing member in its internal space. The reinforcing member lies in the up-and-down direction of the vehicle. Patent Literature 3 states that this will enhance the strength of the bumper beam, and suppress deformation of the bumper beam.